This invention principally relates to the surface of titanium alloy dental implants, although it has application to other types of implants made of titanium alloys. More specifically, the invention relates to roughened surfaces provided on dental implants to improve the osseointegration of the implant surface with the bone, thereby shortening the time between initial insertion of the implant and the installation of a prosthetic tooth.
Various techniques have been suggested for roughening implants, each producing a unique surface. One approach has been to apply materials to the surface of the implant, for example hydroxyapitite, a material that is considered to improve the bonding of the implant to bone because the hydroxyapitite is chemically related to bone. In a related approach, titanium particles have been sprayed onto a titanium implant to roughen the surface. Anodization to add titanium oxides to the surface has also been proposed. Roughening also can be done by removing some of the surface. Grit blasting with fine particles has been proposed to create dents and to abrade away some of the surface. Another method is the use of acid etching to create a roughened surface. At least one supplier of dental implants has proposed grit blasting to create a coarse roughened surface, followed by acid etching to form a superimposed fine roughening.
Etching the surface of titanium with acids has been included in many processes proposed for manufacturing dental implants. In many cases, only general reference to selecting from a list of mineral acids, in other instances specific acids are used. For example, Toho Titanium Co. disclosed in Japanese Published Patent Application JP3146679A1 a two step treatment in which aqueous hydrofluoric acid was used to etch the surface, followed by a second treatment with a solution hydrofluoric acid and hydrogen peroxide. Another example is found in U.S. Published Application 2003/0135282A1, in which an implant is treated with a sequence of three acids—hydrofluoric, sulfuric and hydrochloric acid. The etched surface is coated with plasma before use to improve integration with bone.
In a series of U.S. patents, including U.S. Pat. Nos. 5,603,338; 5,876,453; 5,863,201; and 6,652,765 assigned to Implant Innovations Inc., a unique two-step acid treatment was disclosed, which is used on dental implants to produce an Osseotite® surface. The first acid treatment uses aqueous hydrofluoric acid to remove the “native oxide”, that is, the titanium oxide found on titanium metal surfaces. Removing the native oxide makes the metal surface more accessible to etching by other acids, assuring uniform etching of the titanium surface. Other methods of removing the native oxide could be used, such as plasma treatment, but the initial treatment with aqueous hydrofluoric acid was preferred. The second acid treatment preferably used a mixture of hydrochloric and sulfuric acids to etch the exposed titanium surface. A relatively fine etching was achieved, having peak-to-valley heights of 10 μm or less. The peak-to-peak distance typically is about 1-3 μm. This Osseotite® surface has achieved commercial success, having reduced the time required for osseointegration of the titanium implant with bone.
Previous U.S. patents have shown the titanium surface obtained by scanning electron microscopy (SEM). Another method of describing the surface is surface mapping microscopy (SMM), which produces a computer-generated three-dimensional picture of the region being examined, and several calculated measures of the roughness of the surface. It will be understood by those skilled in the art that acid treatment produces a surface that appears very uniform to the naked eye, but contains variations that become evident only when greatly magnified, as in the photomicrographs. Each region will not be precisely the same as the others, but nevertheless, the variations are small and fall within the general limits discussed above. By carefully controlling the treatment process, each implant has substantially the same surface.
It has more recently been found that, while a consistent response to the two-step acid treatment is obtained on commercially pure titanium, the same treatment process produces non-uniform results on titanium alloys. Because titanium alloys have some benefits over commercially pure titanium, it would be desirable if the topography of the Osseotite® surface were to be duplicated on a titanium alloy surface. To achieve this goal, the inventors found that the process used for commercially pure titanium required unexpected revisions to achieve the desired surface on titanium alloys. Their new process will be described in detail below.